1. Field of the Invention
This invention relates to valve structures.
2. Description of the Prior Art
It has heretofore been known to operate devices via mechanical movements in apparatus which responds to predetermined changes in pressure of fluid applied thereto. See, for example, my U.S. Pat. No. 2,824,919 for "Pressure Responsive Switch," issued Feb. 25, 1958, and U.S. Pat. No. 3,577,793 for "Mechanical Motion Transmitter," issued May 4, 1971. In such apparatus, mechanical movements include a snap action disc spring for operating a movable element such as a pointer or a microswitch plunger. Such elements require very small forces in terms of grams or ounces to effect their operation. Accordingly, the pressure responsive device can be operated with a desired narrow deadband, i.e., the difference between the fluid pressure causing the spring to snap in one direction and the fluid pressure at which the spring snaps back in the opposite direction. Such deadband must be kept narrow in order to maintain high sensitivity in controlling systems. However, this has not been possible with known valve structures that require substantial forces to actuate and reactuate a system, and cannot be driven by such sensitive actuating devices.